This invention relates to a magnetron provided with magnetic field-applying means capable of equalizing the intensity of every portion of a magnetic field applied.
Generally, magnetron is a sort of diode designed to oscillate current introduced across concentric cylindrical cathode and anode electrodes by a magnetic field applied in the axial direction of said electrodes, and is provided with a magnetic field-applying device for applying a magnetic field at right angles to a stream of electrons running across the cathode and anode electrodes. The prior art magnetic field-applying device has a pair of mutually facing permanent magnets so arranged as to enclose an interaction space formed between the cathode and anode electrodes, from above and below, in order to apply a magnetic field at right angles to said interaction space, that is, in the axial direction of the cathode and anode electrodes. The prior art permanent magnets have the mutually facing magnetic pole surfaces made flat. Therefore, a magnetic field applied to the interaction space formed between the mutually facing permanent magnets is ununiformly distributed. Namely, the concentration of a magnetic flux is dense in the interaction space around the center of the mutually facing permanent magnets, but sparse in that portion of the interaction space which is disposed near the peripheral edge of the permanent magnets. Electrons emitted from the cathode electrode to the anode electrode fail to reach the anode electrode through a desired uniform orbit due to the irregular distribution of a magnetic field in the above-mentioned various interaction spaces.
Therefore, the prior art magnetron has the drawbacks that it has a low efficiency of oscillating electric waves and lacks an oscillating stability. If a magnetic field generated by permanent magnets has an ununiform distribution, it will be extremely objectionable particularly to a magnetron which is demanded to produce a high density of magnetic fluxes and a very strong magnetic force.